[425HP409]

The odometer is a direct mechanical drive off of the speedometer cable. You can change the gears in your transmission, or get a reducer adapter to correct this, but any change you make with the odometer will also change what the speedometer reads by the same proportional amount. The problem you have is twofold. 1. The speedometer gears are wrong for your truck with the gearing you have. 2. The speedometer is way off of calibration. If you change your odometer to read correct, the speedo will be really way off. You will not be able to make both of them read correctly with the existing speedometer that you have unless you take the speedometer out and have it calibrated magnetically at a speedo repair shop.